TECHNICAL BASIS FOR ENVIRONMENTAL QUALIFICATION OF SAFETYRELATED MICROPROCESSOR-BASED INSTRUMENTATION AND CONTROL SYSTEMS IN NUCLEAR POWER PLANTS*

摘要

Because of the increasing unavailability of analogrnreplacements for instrumentation and control (I&C) systems andrnthe potential benefits of digital systems, considerable use of thernsuch technology in safety systems of nuclear power plants (NPPs)rnis likely. While digital technology has several advantages and, inrnfact, has been in widespread use in the non-nuclear industry forrnseveral years, a concern with its use in safety-related systems inrnNPPs is the limited experience with the technology in thesernenvironments. This paper summarizes the results of research,rnsponsored by the U.S. Nuclear Regulatory Commission, into thernenvironmental susceptibility of microprocessor-based I&Crnsystems. This research was conducted by the Oak Ridge NationalrnLaboratory (ORNL) and Sandia National Laboratories (SNL) andrnis intended to provide the supporting technical basis forrnenvironmental qualification of safety-related, microprocessor-rnbased I&C equipment in NPPs. ORNL investigated potentialrnfailure modes and vulnerabilities of microprocessor-based interference and radio-frequency interference, temperature,rnhumidity, and smoke exposure. SNL performed smoke exposurerntests on digital components and circuit boards to determine failurernmechanisms and the effect of different packaging techniques onrnsmoke susceptibility.rntechnologies to environmental stressors, including electromagnetic